654 



Rural School Leaflet. 



enough water and bones and other matter useless for food to equal the 

 amount of water in milk. 



The constituents of milk are often referred to as z^vter and total 

 solids. The latter includes all the substances except water, and they col- 

 lect in solid dry form when the water is evaporated, as may be observed 

 by leaving a little milk in a saucer for a short time in a warm place. 

 There are five different substances in the total solids : fat, casein, al- 

 bumen, sugar and ash. It is an interesting exercise to separate them. 

 The chemist can do this with great accuracy, but any person can do it 

 roughly with such aids as are found in the kitchen. A gross analysis 

 of milk may be made as follows : 



For the fat. — ■ Let one quart of fresh milk stand quietly in a pan in a 

 cool place until a rich, clearly-marked layer of cream gathers at the top. 

 This cream is formed by the rising of countless balls or globules of pure 

 milk fat, often called butter-fat, which is distributed evenly through 



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Skimmed milk. 



Fig. 3. — Showing appearance of milk througli high-pozver microscope. 



perfectly fresh milk or milk that is frequently stirred. The fat is so 

 much lighter than the fluid in which it floats that most of it will be found 

 in the cream layer in twelve hours, providing the milk was fresh when 

 "set'' and it has stood undisturbed in a cool place. 



The cream should be removed by skimming or dipping, warmed to 

 about 60° F. and shaken in a bottle which is only partly filled. Soon the 

 fat globules will unite and form light-yellow granules large enough to be 

 seen. The shaking or churning should be continued until as much fat 

 is collected as possible. After it is washed a few times in clean, cold 

 water it is seen in an almost pure state. This fat is the principal constit- 

 uent of butter and also one of the principal constituents of cheese. 



For the casein. — A few drops of acid (or vinegar) should be added to 

 the skimmed milk which was left after the cream was taken off. Soon it 

 will coagulate or thicken. Tt should then be gentlv warmed to about 

 100° F. and carcfulU- broken by a knife or spoon into a few pieces. The 



